Abstract
In this study, the synthesis of polyethylenes has been carried out with titanium-magnesium supported Ziegler-Natta catalysts in laboratory-scale reactors. A correlation of different polymerization conditions with thermal and mechanical properties of polyethylenes has been established. It is seen that there is lowering of molecular weight (Mw), polymer yield, and catalyst activity at high hydrogen pressure and high temperature. The Mw, polymer yield, and catalyst activity are improved with the increase in ethylene pressure. Dynamic mechanical analysis (DMA) results show that the increase in temperature and hydrogen pressure decreases storage modulus. The samples with higher Mw showed high activation energy. The melting point decreases with the increase in hydrogen pressure but increases slightly with the increase in ethylene pressure. It is seen that the increase in reaction temperature, ethylene pressure, and hydrogen pressure leads to an increase in crystallinity. The tensile modulus increases with the increase in hydrogen pressure and can be correlated with the crystallinity of polymer. The Mw has a major influence on the flow activation energy and tensile strength. But the other mechanical and thermal properties depend on Mw as well as other parameters.
Highlights
Polyolefins are prepared commercially using different initiator and catalysts like free radical initiators, Phillips type catalysts, and Ziegler-Natta catalysts
The effect of hydrogen pressure (0, 2, and 5 bar) on molecular weight (Mw) and molecular weight distribution (MWD) has been reported at two different ethylene pressures (5 and 10 bar), polymerization temperatures (60 and 80∘C), and polymerization times (30 and 60 min)
Our observation is in good agreement with the findings made by Moballegh and Hakim [10], where the effect of hydrogen pressure on Mw and MWD has been reported for ethylene/1-butene copolymer [10]
Summary
Polyolefins are prepared commercially using different initiator and catalysts like free radical initiators, Phillips type catalysts, and Ziegler-Natta catalysts. The heterogeneous Ziegler-Natta catalysts remain the main industrial catalysts of choice because of their remarkable ability to affect the polymerization of olefins to produce polymers of high molecular weight and ordered structure [1, 2]. A unique feature of these catalysts is the presence of more than one active site type which leads to polyolefins with broad molecular weight distributions (MWD) and stereoregularity. These distributions influence the physical properties of polyolefins and are responsible for their performance and final applications. The final properties of synthetic polyolefins are affected by different polymerization parameters. Systematic discussions about the International Journal of Polymer Science
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